The amount of heat generated in an inductively coupled cooking vessel is conventionally controlled by varying the frequency of electromagnetic energy or by means of periodic interruption of the electromagnetic energy. However, the controllable range of frequencies is restricted by the upper frequency limit set by the operating characteristic of thyristor switching devices and by the lower frequency limit set by the acoustic sensitivity of the human ears. Therefore, the available power control range is not wide enough to meet a variety of cooking operations. The periodic interruption of the electromagnetic energy, on the other hand, introduces periodic change in voltage of the mains supply if the period of interruption is longer than an appreciable length of time, which could result in flickering of the indoor lighting level when the induction heating apparatus is energized by current supplied from a common source.